Duchenne muscular dystrophy (DMD) is caused by mutations in the dystrophin gene. Dystrophin is a cytoskeletal protein that plays an essential role is assembling the dystrophin-glycoprotein complex. Defects in the assembly or function of the DGC have profound consequences in muscle tissue that lead to many different types of muscular dystrophy. Various lines of evidence indicate that the DGC plays a wide variety of mechanical, structural and signaling roles critical for maintaining normal muscle mass and preventing dystrophic degeneration. Our group has been studying structural determinants of dystrophin (and its paralog utrophin) that mediate interactions with -actin, the ankyrins, -dystrobrevins, -dystroglycan, the sarcoglycans and nitric oxide synthase. We find that the overall organization of the DGC is significantly more complicated than originally thought, and we seek to clarify the structural interactions between different DGC members that contribute to the diverse roles of the complex in skeletal muscle. We have explored the effects of DGC assembly by generating transgenic mice with muscle-specific expression of Dp116, a truncated dystrophin isoform that carries the DGC assembling regions but which lacks actin-binding domains. Surprisingly, expression of the mechanically non-functional Dp116 in severely affected dystrophin:utrophin double knockout (mdx:utrn-/-) mice greatly increases longevity and prevents muscle wasting without affecting the underlying dystrophic histopathology. These data reveal that multiple functions of the DGC and dystrophin can be linked to separate components of the DGC and suggest a surprisingly complex series of functional roles for the complex in skeletal muscle. In this renewal application we propose to continue to dissect the molecular interactions that make up the core of the DGC, to explore the signaling pathways that are targets for the non-mechanical functions of the DGC, and to clarify how the proteins that make up the DGC affect distinct aspects of muscle function. We will also dissect the structural components of utrophin to explore its ability to assemble a functional utrophin-glycoprotein complex to further efforts to use truncated utrophin genes for gene therapy of DMD. Our long range goal is to develop a better understanding of the overall function of dystrophin, utrophin and the DGC and how they work in preventing the pathology associated with multiple forms of muscular dystrophy. By providing greater insight into their functional roles, this work should facilitate th development of therapies for DMD and other forms of muscular dystrophy. PUBLIC HEALTH RELEVANCE: Mutations that affect production of the protein dystrophin are the cause of Duchenne muscular dystrophy, the most common lethal inherited disorder of children. There are large gaps in our understanding of the exact functions that dystrophin plays in muscle cells. This project explores the function of dystrophin and how it controls the function of other muscular dystrophy related proteins, and the results will be important in guiding the development of therapies for the dystrophies.